docs: def get_op(self):
          """Returns all symmetry operations (including inversions and
          subtranslations), but unlike get_symop(), they are returned as
          two ndarrays."""
          if self.centrosymmetric:
              rot = np.tile(np.vstack((self.rotations, -self.rotations)), 
                            (self.nsubtrans, 1, 1))
              trans = np.repeat(self.subtrans, 2*len(self.rotations), axis=0)
          else:
              rot = np.tile(self.rotations, (self.nsubtrans, 1, 1))
              trans = np.repeat(self.subtrans, len(self.rotations), axis=0)
          return rot, trans